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proxy.go
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proxy.go
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package main
import (
"bufio"
"bytes"
"context"
"fmt"
"io"
"io/ioutil"
"log"
"net"
"net/http"
"net/url"
"strings"
)
type ProxyHandler struct {
transport *http.Transport
auth *authenticator
ids chan uint
}
type proxyFunc func(*http.Request) (*url.URL, error)
func NewProxyHandler(proxy proxyFunc, auth *authenticator) ProxyHandler {
return newProxyHandler(&http.Transport{Proxy: proxy}, auth)
}
func newProxyHandler(tr *http.Transport, auth *authenticator) ProxyHandler {
ids := make(chan uint)
go func() {
for id := uint(0); ; id++ {
ids <- id
}
}()
return ProxyHandler{tr, auth, ids}
}
func (ph ProxyHandler) ServeHTTP(w http.ResponseWriter, req *http.Request) {
ctx := req.Context()
ctx = context.WithValue(ctx, "id", <-ph.ids)
req = req.WithContext(ctx)
deleteRequestHeaders(req)
if req.Method == http.MethodConnect {
ph.handleConnect(w, req)
} else {
ph.proxyRequest(w, req, ph.auth)
}
}
func (ph ProxyHandler) handleConnect(w http.ResponseWriter, req *http.Request) {
h, ok := w.(http.Hijacker)
if !ok {
msg := fmt.Sprintf("Can't hijack connection to %v", req.Host)
http.Error(w, msg, http.StatusInternalServerError)
return
}
u, err := ph.transport.Proxy(req)
if err != nil {
http.Error(w, err.Error(), http.StatusInternalServerError)
return
}
var server net.Conn
if u == nil {
server = connectToServer(w, req)
} else {
server = connectViaProxy(w, req, u.Host, ph.auth)
}
if server == nil {
return
}
client, _, err := h.Hijack()
if err != nil {
// The response status has already been sent, so if hijacking fails, we can't return
// an error status to the client. Instead, log the error and finish up.
log.Printf("[%d] Error hijacking connection: %s", req.Context().Value("id"), err)
server.Close()
return
}
// Kick off goroutines to copy data in each direction. Whichever goroutine finishes first
// will close the Reader for the other goroutine, forcing any blocked copy to unblock. This
// prevents any goroutine from blocking indefinitely (which will leak a file descriptor).
go func() { io.Copy(server, client); server.Close() }()
go func() { io.Copy(client, server); client.Close() }()
}
func connectViaProxy(w http.ResponseWriter, req *http.Request, proxy string, auth *authenticator) net.Conn {
// can't hijack the connection to server, so can't just replay request via a Transport
// need to dial and manually write connect header and read response
conn, err := net.Dial("tcp", proxy)
if err != nil {
http.Error(w, err.Error(), http.StatusInternalServerError)
return nil
}
err = req.Write(conn)
if err != nil {
log.Printf("[%d] Error sending CONNECT request: %v", req.Context().Value("id"), err)
http.Error(w, err.Error(), http.StatusInternalServerError)
return nil
}
rd := bufio.NewReader(conn)
resp, err := http.ReadResponse(rd, req)
if err != nil {
conn.Close()
http.Error(w, err.Error(), http.StatusInternalServerError)
return nil
} else if resp.StatusCode == http.StatusProxyAuthRequired && auth != nil {
resp.Body.Close()
conn.Close()
conn, err = net.Dial("tcp", proxy)
if err != nil {
http.Error(w, err.Error(), http.StatusInternalServerError)
return nil
}
rd = bufio.NewReader(conn)
resp, err = auth.connect(req, conn, rd)
if err != nil {
http.Error(w, err.Error(), http.StatusInternalServerError)
return nil
}
}
copyResponseHeaders(w, resp)
w.WriteHeader(resp.StatusCode)
if resp.ContentLength != -1 {
// Only copy/close the response body when there is a known ContentLength.
// Otherwise, assume that anything that comes after the header is tunnelled data
// that is not part of the response itself.
//
// Sometimes, a CONNECT response has no Content-Length header (in which case Go's
// net/http library will set resp.ContentLength to -1). When this happens, reading
// or closing resp.Body will block, possibly indefinitely.
if n, err := io.CopyN(w, resp.Body, resp.ContentLength); err != nil {
log.Printf("Error copying response body (copied %d/%d bytes): %v",
n, resp.ContentLength, err)
}
resp.Body.Close()
}
if resp.StatusCode != http.StatusOK {
conn.Close()
return nil
}
return conn
}
func connectToServer(w http.ResponseWriter, req *http.Request) net.Conn {
// TODO: should probably put a timeout on this
conn, err := net.Dial("tcp", req.Host)
if err != nil {
http.Error(w, err.Error(), http.StatusInternalServerError)
return nil
}
w.WriteHeader(http.StatusOK)
return conn
}
func (ph ProxyHandler) proxyRequest(w http.ResponseWriter, req *http.Request, auth *authenticator) {
// Make a copy of the request body, in case we have to replay it (for authentication)
var buf bytes.Buffer
n, err := io.Copy(&buf, req.Body)
if err != nil {
log.Printf("Error copying request body (got %d/%d): %v", n, req.ContentLength, err)
w.WriteHeader(http.StatusInternalServerError)
return
}
rd := bytes.NewReader(buf.Bytes())
req.Body = ioutil.NopCloser(rd)
resp, err := ph.transport.RoundTrip(req)
if err != nil {
http.Error(w, err.Error(), http.StatusInternalServerError)
return
}
defer resp.Body.Close()
if resp.StatusCode == http.StatusProxyAuthRequired && auth != nil {
_, err = rd.Seek(0, io.SeekStart)
if err != nil {
log.Printf("Error while seeking to start of request body: %v", err)
} else {
req.Body = ioutil.NopCloser(rd)
resp, err = auth.do(req, ph.transport)
if err != nil {
http.Error(w, err.Error(), http.StatusInternalServerError)
return
}
defer resp.Body.Close()
}
}
copyResponseHeaders(w, resp)
w.WriteHeader(resp.StatusCode)
_, err = io.Copy(w, resp.Body)
if err != nil {
// The response status has already been sent, so if copying
// fails, we can't return an error status to the client.
// Instead, log the error.
log.Printf("[%d] Error copying response body: %s", req.Context().Value("id"), err)
return
}
}
func deleteConnectionTokens(header http.Header) {
// Remove any header field(s) with the same name as a connection token (see
// https://tools.ietf.org/html/rfc2616#section-14.10)
if values, ok := header["Connection"]; ok {
for _, value := range values {
if value == "close" {
continue
}
tokens := strings.Split(value, ",")
for _, token := range tokens {
header.Del(strings.TrimSpace(token))
}
}
}
}
func deleteRequestHeaders(req *http.Request) {
// Delete hop-by-hop headers (see https://tools.ietf.org/html/rfc2616#section-13.5.1)
deleteConnectionTokens(req.Header)
req.Header.Del("Connection")
req.Header.Del("Keep-Alive")
req.Header.Del("Proxy-Authorization")
req.Header.Del("TE")
req.Header.Del("Upgrade")
}
func copyResponseHeaders(w http.ResponseWriter, resp *http.Response) {
for k, vs := range resp.Header {
for _, v := range vs {
w.Header().Add(k, v)
}
}
// Delete hop-by-hop headers (see https://tools.ietf.org/html/rfc2616#section-13.5.1)
deleteConnectionTokens(w.Header())
w.Header().Del("Connection")
w.Header().Del("Keep-Alive")
w.Header().Del("Proxy-Authenticate")
w.Header().Del("Trailer")
w.Header().Del("Transfer-Encoding")
w.Header().Del("Upgrade")
}